A bit of googling came up with a great web site:
http://www.alice-in-wonderland.net/alice.html
the PDF copies there look to be pretty good, but aren't ideally formatted for reading on a 5 or 6 inch reader. I took those copies and trimmed the margins as far as I could, which should help a bit (attached below.)
This isn't available as an ebook, but if you are interested in Lewis Carroll you really owe it to yourself to pick up a copy of The Annotated Alice:
http://www.amazon.com/Annotated-Alic...dp/0393048470/